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Sensor device to record speed and motion direction of an object,
especially rotational speed and direction of a rotating object

Abstract

A sensor device to record the speed and motion direction of an object,
especially rotational speed and direction of a rotating object, based on
the magnetoresistive effect, is provided with a magnetic field generator
(2, 15) coupled to object (1), which generates a locally and time-defined
varying reference magnetic field (H), with two magnetic field sensors
(SE1, SE2) made of a magnetoresistive material, which are positioned at a
stipulated spacing (.DELTA.y) from each other relative to magnetic field
generator (2, 15) so that they are traversed by magnetic field components
(H.sub.1, H.sub.2) of the reference field (H) that are phase shifted
relative to each other, in which the phase shift .DELTA..PHI. is not
equal to an integer multiple of 90.degree., and with a signal processing
circuit (5), which records the magnetoresistive resistance (R_MR1, R_MR2)
of the magnetic field sensors (SE1, SE2) dependent on the magnetic field
components (H.sub.1, H.sub.2) in the magnetic field sensors (SE1, SE2)
and generates from it electrical signals representative of the rotation
speed and direction (U.sub.s).

1. Sensor device for determination of speed and motion direction of an
object, especially rotational speed and direction of a rotating object
based on the magnetoresistive effect with a magnetic field generator (2,
15) coupled to the object (1), which generates a locally and time-defined
varying reference magnetic field (H), two magnetic field sensors (SE1,
SE2) made of a magnetoresistive material, which are positioned at a
stipulated spacing (.DELTA.y) relative to each other relative to magnetic
field generators (2, 15) so that they are traversed by magnetic field
components (H.sub.1, H.sub.2) of reference field (H) that are phase
shifted relative to each other, in which the phase shift (.DELTA..PHI.)
is not equal to a whole number multiple of 90.degree., and a signal
processing circuit (5), which determines the magnetoresistive resistance
(R_MR1, R_MR2) of magnetic field sensors (SE1, SE2) dependent on the
magnetic field components (H.sub.1, H.sub.2) in the magnetic field
sensors (SE1, SE2) and generates from it electrical signals (U.sub.s)
representative of the speed and motion direction, especially rotational
speed and direction of object (1), characterized by the fact that the
signal processing circuit (5) has a voltage difference formation circuit
(6) to form the difference (U.sub.d) of the magnetic field-dependent
voltages (U.sub.1, U.sub.2) diminishing on the magnetic field sensors
(SE1, SE2) and a digitization circuit (8) connected after the voltage
difference formation circuit (6) for the difference voltage (U.sub.d), in
which the pulse duty factor of the digital signal (U.sub.s) generated by
the digitization circuit (8) is evaluable by an evaluation circuit as a
criterion for rotational direction (D1, D2) of object (1).

2. Sensor device according to claim 1, in which the magnetic field
generator is a multipole wheel (2) with alternating magnetic poles (N, S)
that generate an essentially sinusoidally varying magnetic field (H)
around the wheel periphery.

3. Sensor device according to claim 1, in which the magnetic field
generator is a generator wheel (15) rotating in the field of a permanent
magnet (16) with a profiling (14) that varies the magnetic field (H).

4. Sensor device according to one of the claims 1 to 3, in which the two
mag-netic sensors (SE1, SE2) are positioned essentially parallel on a
common chip carrier (3).

5. Sensor device according to one of the claims 1 to 4, in which the two
magnetic field sensors (SE1, SE2) traversed by a constant current
(I.sub.MR) are electrically connected in series.

6. Sensor device according to one of the claims 1 to 5, in which a
switchable current source (9) for signal transmission in the
two-conductor technique, controlled by the digital signal (U.sub.s) of
digitization circuit (8) is connected after signal processing circuit
(5).

7. Sensor device according to one of the claims 1 to 6, in which the
magnetic field sensors (SE1, SE2) are arranged with the signal processing
circuit (5) on a common chip carrier (3).

8. Sensor device especially according to one of the claims 1 to 7, in
which each maagnetic field sensor (SE1, SE2) is provided with a current
conductor (A11, A12) to conduct an auxiliary current (I.sub.k1,
I.sub.k2), which generates in the corresponding magnetic field sensor
(SE1, SE2) a constant magnetic field (H.sub.Ik1, H.sub.Ik2) superimposed
on the magnetic field (H) being determined.

9. Sensor device according to claim 8, in which the current conductor
(A11, A12) is arranged loop-like to generate the constant magnetic field.

10. Sensor device according to one of the claims 1 to 9, in which the
magnetic field generator (2') is provided with opposite magnetic poles
(N1, N2, N3; S1, S2, S3) to recognize the absolute position of generator
(2').

11. Sensor device especially according to one of the claims 1 to 10, in
which the magnetic field sensors (SE1, SE2) determine the signal trend
during passage of a magnetic pole (N) of magnetic field generator (17)
with high time resolution to recognize the absolute position of generator
(17).

12. Sensor device according to claim 11, in which the magnetic field
generator includes a single permanent magnet (17).

Description

[0001] The invention concerns a sensor device to record speed and motion
direction of an object, especially rotational speed and direction of
rotation of a rotating object based on the magnetoresistive effect.

[0002] As background to the invention and prior art, it can be stated that
the magnetoresistive (AMR) effect, under which the so-called anisotropic
magnetoresistive effect and the "giant magnetoresistive effect" fall,
permits measurement of magnetic fields. The AMR effect, which is used
below as representative for the necessary explanations, occurs in
ferromagnetic materials whose electrical conductivity depends on the
angle between electrical current density and magnetization of the
ferromagnetic material. External magnetic fields can therefore alter the
electrical resistance of a magnetoresistive layer, since magnetization is
rotated out of the so-called "easy direction", i.e., the direction of
preferred magnetization, by such external magnetic fields.

[0003] Strip-like layers of the ferromagnetic material are then
essentially used as sensors based on the AMR effect. Because of the shape
anisotropy of the magnetoresistive layer stipulated by the strip layer
configuration (length>width>>thickness applies for strips) the
magnetization vector always lies in the plane of the layer. The layer
generally consists of a 20 nm to 80 nm thick layer of the permalloy alloy
Ni.sub.81Fe.sub.19. The maximum obtainable relative resistance changes
amount to about 3.5%. The external magnetic field is also applied in the
so-called magnetically "hard direction"--the direction of width of the
sensor strip.

[0004] If the resistance change resulting from application of a magnetic
field in the width direction is plotted on a magnetic field/resistance
change diagram, a typical bell curve is obtained around the value 0 of
the magnetic field. The electrical resistance is greatest for an angle 0
for electrical current density and magnetization and smallest for an
angle of 90.degree.. Because of this characteristic the sensitivity of
the sensor for small magnetic fields is very small in the width direction
of the strip. Because of the bell curve, the characteristic is also
indistinct, since the corresponding magnetic field for a certain
resistance change can lie parallel or antiparallel to the width
direction. Linearization is therefore necessary for sensor application,
especially when the sensor is used to determine the absolute value of the
magnetic field. As was explained at length in the German Unexamined
Patent Application DE 198 10 218 A1 of the applicant, referred to as
closest prior art, such linearization is possible by so-called "barber
pole" or by applying a magnetic field that overlaps the magnetic field
being measured in the magnetically "hard" direction. The overlapped
magnetic field can be generated by a permanent magnet or by a current
conductor lying parallel to the magnetoresistive strip layer and kept
insulated from it. Compensation of the effect of external magnetic fields
on the sensor strip during widening of the measurement range and
amplification of the output signal of the sensor are also an advantage
for absolute measurement, as is also explained at length in the
aforementioned document.

[0005] For application as a rotational speed sensor, it is sufficient to
allocate two at least linearized magnetic field sensor strips to a
magnetic multipole wheel rotatable relative to them, in which the sensor
strips are arranged at an angle to each other that corresponds to an
integer multiple of the pole division of the multipole wheel. The two
magnetic field sensors are therefore traversed by the same magnetic
field, which oscillates because of rotation of the object being recorded.
Thus, there is no phase shift between the resistance changes generated in
the sensor strips. The latter can be converted finally into corresponding
frequencies and thus rotational speed of the multipole wheel by
conversion to voltage signals and digitization.

[0006] A shortcoming in the rotational speed recording device demonstrated
from DE 198 10 218 A1 is the fact that recognition of direction of
rotation does not occur. For many applications of such rotational speed
sensors, however, it is quite important to recognize the direction of
rotation, for example, in order to select whether a machine or vehicle is
running forwards or backwards.

[0007] It is also stated that voltage signals are generated and
transmitted in the circuitry shown in DE 198 10 218 A1. The sensor
devices depicted there and their circuits are therefore only marginally
suited for modern vehicle technology, which is increasingly switching to
the transmission of current signals with a signal level of, say, 7 mA and
14 mA.

[0008] The underlying task of the invention is therefore to offer a sensor
device to record the speed of an object, especially the rotational speed
of a rotating object, based on the magnetoresistive effect, which also
permits recognition of the direction of movement, especially the
direction of rotation of the object.

[0009] The solution to this task is offered by the features of claim 1.
The key feature is positioning of the two magnetic field sensors at a
stipulated spacing from each other relative to the magnetic field
generator so that the two sensors are traversed by magnetic field
components of the reference field phase shifted relative to each other.
The phase shift should then preferably be unequal to 0.degree.,
90.degree., 180.degree., . . . i.e., unequal to integer multiples of
90.degree..

[0010] Based on the mentioned phase shift of the magnetic field components
in the two sensor strips, different magnitudes of the magnetic field
components are obtained at each measurement time in the sensor strip so
that selective evaluation of direction of rotation is possible by
corresponding signal processing. The description of the practical example
is referred to for better understanding in this connection.

[0011] Preferred variants of the invention are mentioned in the subclaims.
The electrical series circuit of magnetic field sensors traversed by
constant current is emphasized in particular here, which permits
operation of the sensor device with the so-called two-conductor
technique. Here again the description of the practical examples is
referred to for further understanding, which is provided below with
reference to the accompanying drawings. In the drawings:

[0013] FIG. 2 shows a schematic perspective view of two magnetic field
sensor strips on a chip carrier in a first variant,

[0014] FIG. 3 shows a schematic diagram of the magnetic field trend of the
multipole wheel versus time according to FIG. 1,

[0015] FIG. 4 shows a block diagram of a sensor device with two magnetic
field sensors and a signal processing circuit in a two-conductor
technique,

[0016] FIG. 5 shows a time diagram of a magnetic field of a multipole
wheel,

[0017] FIGS. 6 and 7 show oscilloscope recordings of analog and digital
voltage signals generated by the signal processing device in different
directions of rotation,

[0018] FIG. 8 shows a block diagram of a sensor device with signal
processing circuit in a second variant,

[0019] FIG. 9 shows a schematic perspective view of two magnetic field
sensors arranged on a chip carrier with current conductors to generate an
auxiliary magnetic field,

[0020] FIGS. 10 and 11 show block diagrams of sensor devices according to
FIG. 9 with signal processing circuits in the two-conductor technique or
ordinary technique,

[0021] FIG. 12 shows a schematic perspective view of a magnetic field
sensor with a current conductor applied in a spiral shape to generate an
auxiliary magnetic field,

[0022] FIG. 13 shows a schematic view of a magnetic field generator with a
profiled generator wheel and permanent magnet,

[0023] FIG. 14 shows a schematic view of a multipole wheel with a sensor
device in a second variant,

[0024] FIG. 15 shows a time diagram of the magnetic field of the multipole
wheel according to FIG. 14,

[0025] FIG. 16 shows an oscilloscope recording of the analog and digital
voltage signal as generated by the signal processing device in an
arrangement according to FIG. 14,

[0026] FIG. 17 shows a schematic view of a single permanent magnet as
magnetic field generator with sensor device and

[0027] FIG. 18 shows an oscilloscope recording of the analog and digital
voltage signals generated by the signal processing device in the
arrangement according to FIG. 17.

[0028] The basic design of a sensor device to record rotational speed and
direction of a rotating object is to be explained from FIG. 1. The
rotating object, for example, can be a vehicle wheel or a machine part.
For the present description it is assumed in the interest of simplicity
that a shaft 1 is involved. A so-called multipole wheel 2 is coupled to
rotate in unison with this shaft 1, which lies in direction z or is
coupled to it via a corresponding gear coupling with a specified gear
ratio, which, as a magnetic field generator, generates a locally and
time-defined varying reference magnetic field H through alternating north
and south poles N, S on its periphery. These opposite magnetic poles
alternate with each other on the periphery of multipole wheel 2 with
constant spacing B. A reference magnetic field H, which varies in time
through rotation of the multipole wheel, therefore forms in the
peripheral direction .PHI., i.e., varying locally in sinusoidal or
cosinusoidal fashion.

[0029] The example just sketched concerns recording of rotational speed
and direction of a rotating object. However, quite generally the sensor
device according to the invention can also be used for linearly moved
objects to record their speed and direction of motion. Linearly moved
supports and slides of machine tools can be mentioned as examples. A
linear arrangement of alternating magnetic poles is then chosen in these
as magnetic field generator, these poles then varying also sinusoidally
or cosinusoidally along the scale. By motion of the object with the scale
attached to it, the reference magnetic field then also varies in time.
The following description of the practical example according to FIG. 1 is
therefore also gleaned from the preceding case.

[0030] A chip carrier 3, on which two ordinary magnetic sensors SE1, SE2
from a magnetoresistant material are arranged at a stipulated spacing Ay
relative to each other is arranged in radial direction r at a spacing a.
The direction of spacing Ay runs in the peripheral direction .PHI..

[0031] As is apparent from FIG. 2, the two magnetic field sensors SE1, SE2
are each strips of a ferromagnetic material having strong shape
anisotropy. Length l is therefore greater than width b which is much
greater than thickness d for each strip. If an electric current IMR1,
IMR2 is now passed through such a layer in the direction of length l, the
resistance depends on angle .theta. between the vectors of the electrical
current density J and magnetization M. External magnetic fields H.sub.1,
H.sub.2 can alter the electrical resistance R.sub.13 MR1. R.sub.13 NMR2
in the layer because of this. This results from rotation of magnetization
M from the so-called magnetically "easy" direction, i.e., the direction
of preferred magnetization, which in FIG. 2 is the x direction of the
shown coordinate system. The y direction is the magnetically "hard"
direction. By measuring the magnetoresistive resistance R_MR1 and
R.sub.13 MR2 via a corresponding signal processing circuit, as will be
further explained with reference to FIG. 4 among others, representative
electrical signals can be generated for the rotational speed of multipole
wheel 2 and consequently shaft 1.

[0032] As is apparent from FIGS. 1 and 3 in this connection, by
positioning the two magnetic field sensors SE1, SE2 at a spacing .DELTA.y
in front of the end of the opposite magnet poles N, S of multipole wheel
2, these sensors are traversed by two magnetic field components H.sub.1,
H.sub.2 that are phase shifted relative to each other. At a specified
time to, the magnetic field H.sub.1(t.sub.0), for example, is maximal,
whereas the magnetic field H.sub.2(t.sub.0) in the second magnetic field
sensor SE2 at this time is precisely zero. The corresponding magnetic
field components H.sub.1 and H.sub.2 are therefore shifted relative to
each other by a specific phase shift ".DELTA..PHI.location". At time
t.sub.1 the negative, i.e.. oppositely directed magnetic field
H.sub.1(t.sub.1) prevails in magnetic field sensor SE1, whereas in sensor
SE2 the positive magnetic field H.sub.2(t.sub.1) is present. By rotating
the multipole wheel with a specific number of rotations, a resistance
trend is thus obtained in each magnetic field sensor SE1, SE2 that is
determined by the difference magnetic field varying owing to rotation in
time-defined fashion.

[0033] With the signal processing circuit depicted in FIG. 4, which can be
integrated on chip carrier 3, the magnetoresistive resistance R.sub.13
MR1, R.sub.1MR2 varied by the magnetic field components H.sub.1, H.sub.2
in the two magnetic field sensors SE1, SE2 can be recorded and electrical
signals representative of the rotational speed and direction of multipole
wheel 2 or shaft 1 generated from it. For this purpose the two
magnetoresistive resistances R.sub.13 MR2, R.sub.13 MR2 [sic] are
connected in series to a constant current source 4 so that the currents
IMR1, IMR2 (FIG. 2) through resistances R.sub.13 MR1, R.sub.13 MR2 are
equal to each other and correspond to the total current IMR.sub.13 tot.

[0034] The signal processing circuit 5 measures the voltage U.sub.1,
U.sub.2 dropping over resistances R.sub.13 MR1 and R.sub.13 MR2 and
supplies it to a voltage difference formation circuit 6 and a measurement
amplifier 7. A voltage U.sub.0=v(U.sub.1-U.sub.2) is formed, in which v
is the amplification factor. The difference voltage U.sub.0 is sent to a
connected digitization circuit 8 in the form of a Schmitt trigger so that
the output voltage U.sub.3 is formed. With it a switchable current source
9 can be connected whose low level is 0 mA and whose high level is 7 mA.
This digitized current signal I.sub.p is superimposed with the total
current IMR.sub.13 tot to a digitized current signal I.sub.tot with two
levels of 7 mA and 14 mA, which can be evaluated, for example, by a
central control unit in a vehicle. This type of signal transmission is
also referred to as the two-conductor technique, since only two line
connections are necessary in it to supply the corresponding components
and for signal transmission.

[0035] An example of the signal trend of the sensor device depicted in
FIG. 4 is shown in FIGS. 5 to 7. The action and effect of spacing
.DELTA.y and the related phase shift .DELTA..PHI., location between the
two magnet field sensors SE1, SE2 and R.sub.13 MR1, R.sub.13 MR2 can be
explained with it. A cosinusoidal magnetic field H.sub.100 is assumed,
whose maximum amplitude is 3000 A/m (see FIG. 5). The frequency of the
magnetic field is 50 Hz, which means that under the assumption that 10
magnetic pole pairs N-S are distributed on the periphery, the multipole
wheel rotates with a frequency of 5 Hz. The spacing is set so that the
phase shift .DELTA..PHI. should lie at +20.degree.. The dashed curve
trend depicted in FIG. 6 is obtained as analog output voltage U.sub.a.
During digitization of this voltage U.sub.a by means of a Schmitt
trigger, the digital signal U.sub.s marked with a solid line in FIG. 6 is
generated. The switching thresholds of the Schmitt trigger during
conversion to the digital signal U.sub.s then lie at 1.55 V from low to
high level for rising U.sub.a and at 1.20 V for the transition from high
to low for falling. As is apparent from FIG. 6. the "unsymmetric" trend
of U.sub.3, i.e., the fact that the phase difference .DELTA..PHI.,
location must not equal 90.degree., leads to differently long high and
low phases of U.sub.a. In the output signal a different pulse duty factor
(i.e., t.sub.high/t.sub.low) is thus obtained for the two levels. In
rotation direction D1 (FIG. 1) a pulse duration t.sub.high of about 8 ms
and t.sub.low of about 2 ms is obtained. The pulse duty factor
t.sub.high/t.sub.low is therefore 4.

[0036] In rotation direction D2 (FIG. 1) in the opposite direction a phase
shift .DELTA..PHI., location =-20.degree. is obtained so that the signal
trend shown in FIG. 7 for the analog output signal U.sub.a (dashed line)
and the digital signal Us formed from it (solid line) are formed. The
same switching thresholds were again used. As can be gathered from FIG.
7, the pulse duration for the high level thigh in this case is about 2 ms
and t.sub.low is about 8 ms so that t.sub.high/t.sub.low=0.25.

[0037] As is apparent from a comparison of FIGS. 6 and 7, the rotational
speed of the multipole wheel 2 can be determined, on the one hand, from
the agreeing frequency of the digital signal U.sub.s. The following
approximation should then always apply. The rotational speed during a
pole change, i.e., t.sub.high+t.sub.low remains almost constant. The
representative electrical signal for the rotation direction that is
evaluable accordingly is obtained via the pulse duty factor. It is
pointed out that FIGS. 5 to 7 only show examples.

[0038] The magnitude of magnetic field H.sub..PHI. need not amount to 3000
A/m in order to permit clear detection of the rotational speed direction.
This depends primarily on the magnetic field sensitivity of the sensor
elements SE1, SE2, which is stipulated in the AMR effect mostly by the
geometry of the two magonetoresistive strips. However, the amplitude of
voltage U.sub.a rises with increasing magnetic field up to a saturation
point.

[0039] The frequency doubling because of the nonlinear characteristic of
the AMR effect, i.e., f.sub.Ua=F.sub.Us=2.multidot.(fH.sub.101) should
also be noted. It is further pointed out that the magnetic field sensors
SE1 and SE2 are arranged so that the magnetic field H being measured at
the location of the magnetoresistive layers is of different size.

[0040] The two magnetic field sensors SE1, SE2 in the practical example of
the sensor device depicted in FIG. 8 are connected electrically in
parallel with their magnetoresistive layers R_MR1 and R_MR2 and are
supplied with a constant current I.sub.MR1 and I.sub.MR2 from a constant
current source 4, 4'. The voltage drop over the two magnetic field
sensors R_MR1, R_MR2 is determined by taps 10, 11, between which the
difference voltage U.sub.d prevails. To this extent the voltage
difference formation circuit drops out of the practical example according
to FIG. 4. Only a measurement amplifier 7 and a digitization circuit 8
are again provided in order to generate a digital output signal U.sub.s.
This is again evaluable accordingly in order to determine the rotational
speed and direction of multipole wheel 2.

[0041] As is already known in principle from DE 198 10 218 A1 mentioned in
the introduction, the magnetic field sensors SE1, SE2 can also be
provided with linearization, in which auxiliary current conductors A11
and A12 are arranged parallel to the magnetoresistive resistors R_MR1 and
R_MR2 separately via an insulation layer 12. These auxiliary conductors
are wired so that they are traversed by opposite currents I.sub.k1 and
I.sub.k2, which generate a magnetic field H_Ik1 or H_Ik2 superimposed on
the magnetic field components H.sub.1, H.sub.2 in the two sensor strips
SE1, SE2. As shown in FIG. 9, because of the opposite directions of
currents I.sub.k1 and I.sub.k2, the two auxiliary magnetic fields
H.sub.13 Ik1 and H_Ik2 are directed oppositely. The magnetic field
components H.sub.1 and H.sub.2 originating from the multipole wheel
therefore need no longer be of different size in order to be able to
conduct a rotational speed and direction-sensitive measurement. The
magnetic fields H_Ik1 and H.sub.13 k2 overlap first additively (H_Ik2)
and then subtractively (H.sub.13 IK1) with the magnetic field H.
Different total values for H.sub.tot1 and H.sub.tot2 are obtained. This
is particularly advantageous when an appropriate value for the phase
difference .DELTA..PHI., location of the sensors SE1, SE2 cannot be
achieved on a chip carrier 3 for reasons of space. Because of magnetic
fields H_Ik1 and H_Ik2, the phase shift .DELTA..PHI., location prescribed
according to claim 1 between the phase-shifted magnetic field component
can also be an integer multiple of 90.degree..

[0042] A wiring and evaluation circuit for the variant of the invention
shown in FIG. 9 is depicted in FIG. 10. The auxiliary conductors A11, A12
symbolized by resistors R_k1 and R_k2, as well as the magnetoresistive
resistors R_MR2 and R_MR1 of the two magnetic field sensors SE1, SE2 are
again shown here in series in a constant current source 4. The measured
voltages U1, U2 again diminish over the latter, which are processed by a
voltage difference formation circuit 6, a measurement amplifier 7 and a
digitization circuit 8 in the form of a Schmitt trigger. The output
signal of the Schmitt trigger 8 drives a switchable current source 9 in
the already mentioned fashion. Through a parallel branch 13 to the two
auxiliary conductors A11, A12, these auxiliary conductors can be bridged
by closing the switch S in parallel branch 13. The situation then
corresponds to the circuit according to FIG. 4.

[0043] Auxiliary conductors A11, A12, which are symbolized in FIG. 11 by
the resistors R_k1 and R_k2 connected in series, can again also be used
similarly to FIG. 8 in the parallel connected magnetoresistive resistors
R_MR1 and R_MR2. These two resistors are again bridged via a parallel
branch 13 with switch S. Otherwise, the description of FIG. 8 can be
referred to in conjunction with the rest of the circuit, the
corresponding components being provided with identical reference numbers.

[0044] FIG. 12 schematically depicts that an auxiliary conductor A11 can
also be implemented via a magnetoresistive resistor R_MR1 through a
conducting path applied to the insulation layer 12 in several loops.
Current multiplication and thus an increase in additive magnetic field
occurs because of this.

[0045] In the practical example depicted in FIG. 13, a magnetic field
generator is used in which a magnetic generator wheel 15 with a toothed
outer profile 14 moves in the field of a permanent magnet 16. The
material of generator wheel 15 varies the field of the permanent magnet
16 so that during rotation of generator wheel 15 a locally and
time-defined varying reference magnetic field is again generated. This
can be detected by the magnetic field sensors SE1, SE2 in the same manner
as described above.

[0046] FIG. 14 shows a preferred variant of the sensor device according to
the invention in which the absolute position of multipole wheel 2' and
thus shaft 1 is recognizable. As is apparent from the depiction, the
magnetic poles are no longer equidistant, but distributed with nonuniform
spacings or widths over the periphery of multipole wheel 2'. The
peripheral length of the magnetic poles N1, S1 thus constantly diminishes
via N2, S2 to N3, S3, etc. A magnetically coded multipole wheel 2'
configured in this way generates the magnetic field H.PHI. depicted in
FIG. 15 during rotation DR in the peripheral direction .PHI.. If this
magnetic field is evaluated by means of the magnetic field sensors SE1,
SE2 on chip carrier 3 with an evaluation circuit similar to FIGS. 3 and
7, the signal trend of voltages U.sub.a and U.sub.s depicted in FIG. 16
is obtained during the phase shift of .DELTA..PHI., location=+20.degree..
As follows from the time-resolved depiction, the time length t.sub.high
varies while the signal is situated at the high level. Because of the
accompanying variation in pulse duty factor, the conclusion can be drawn
concerning the absolute position of the multipole wheel. The approach to
an almost constant rotation speed during the period t.sub.high+t.sub.low
should then apply again.

[0047] Finally, in conjunction with FIGS. 17 and 18 a special application
of the sensor device according to the invention will be explained, which
can actually be considered the limiting case of speed and motion
direction determination described according to the invention Thus, in the
extreme case of the signal trend, on passing by a magnetic pole N of the
magnetic field generated, for example, by a single permanent magnet 17,
it can be determined with high time resolution that the absolute position
of the generator can be recognized at least within certain limits. During
the passage shown in FIG. 17 with arrow 18 of permanent magnet 17 on the
two magnet sensors arranged at "phase shift spacing" .DELTA.y, during
evaluation similar to FIGS. 4 to 7, we again obtain the signal trend
shown in FIG. 18 of the voltages U.sub.a and U.sub.s. The "microposition"
can be determined via the time sequence of the signal, in which the
output voltage U.sub.a characteristically reveals three positions 1, 2
and 3 between the end positions A and B. A linear movement of the
permanent magnet in the vicinity of magnetic field sensors SE1, SE2 can
be detected with different positions because of this if the output
positions, namely positions A and B are known. The precise number of
differentiable positions depends on the number and orientation of the
employed permanent magnets and the magnetic fields. Moreover, by using
additional sensors and their appropriate arrangement, additional
positions can be recognized. The permanent magnet 17 passed by magnetic
field sensors SE1, SE2 can also be rotated by 90.degree. so that the
"north/south pole axis" lies in the direction of motion.